Fats and fatty oils, commonly called triglycerides, are constituted of triesters of glycerol, and include minor amounts of fatty acids. At ambient temperatures, usually in the range of about 20.degree. to about 25.degree. C., fats are solids, whereas fatty oils are liquids.
Triglycerides are widely distributed in nature. Some triglycerides are edible while others are not. Many are derived directly from vegetable, animal, and marine sources. Others are obtained, as by-products, in the production of fiber from vegetable matter, and in the production of protein from vegetable, animal or marine matter.
Edible vegetable oils include canola, coconut, corn germ, cottonseed, olive, palm, peanut, rapeseed, safflower, sesame seed, soybean, and sunflower oils. Examples of nonedible vegetable oils are jojoba oil, linseed oil and castor oil.
Illustrative sources of edible animal-derived oil include lard and tallow. Examples of nonedible animal-derived oil are low grade tallow and neat's-foot oils.
Some of these oils may have the color that is objectionable to a consumer. Thus, the oil needs to be bleached to improve its color quality. To this end, a great many oils are commonly treated with bleaching clays to reduce oil color values by adsorptive purification. Bleaching clays generally improve oil color quality by adsorbing color impurities that are present. Color impurities typically present in oils include, for example, carotenoids, xanthophylls, xanthophyll esters, chlorophyll, tocopherols, as well as oxidized fatty acids and fatty acid polymers.
It is also desirable to remove color impurities from a nonedible oil to obtain a desirable color.
Natural clays, e.g., Fuller's earth and the bentonites, have commonly been used as bleaching clays to remove both the naturally-occurring and the otherwise-present, e.g., the thermally-induced, color impurities from edible and nonedible oils. It has been suggested that clays containing a zeolite can be used for such a purpose as well.
Kaolin clays, on the other hand, have proven to be poor bleaching clays under various conditions. This is due, in part, to the fact that kaolin clays are considered non-intercalating, with the exception of halloysite which occurs in nature as a very unstable hydrate. See, e.g., van Olphen, H., An Introduction to Clay Colloid Chemistry, 2nd ed., Wiley-Interscience Publication (1977); p. 186.
U.S. Pat. No. 2,934,504 to Talvenheimo discloses the use of kaolin clays as catalysts for the cracking of hydrocarbons. In every example Talvenheimo teaches a treatment method which subjects the kaolin clay to drying conditions of four hours at 1350.degree. F. (732.degree. C.). The teaching of this drying treatment exemplifies the great differences between bleaching activity, the object of the present invention, and catalytic activity, the object of the Telvenheimo patent.
Acid-activated clays have been used for bleaching oils. Such clays generally remove a relatively wider spectrum of color impurities.
A conventional process for producing acid-activated bleaching clays utilizes calcium bentonite clays and sulfuric acid. The calcium bentonites used in the acid activation process typically are neutral to mildly basic. The acidic salts formed during activation and residual acid can be washed off and separated by filtration from the product clay, if desired. However it is not necessary to do so.
Another type of naturally-occurring clay, frequently classified as palygorskite clays, requires heat to impart bleaching activity. Mineralogically, the palygorskite clays are distinguishable from the bentonites (smectites or montmorillonites).